1. Field of the Invention
This invention relates to the process by which three-dimensional images, moving or stationary, may be transformed and transmitted, and then reconstructed for viewing purposes by the use of optical wavelength reconstruction techniques; and particularly to the use of holograms for said purposes.
2. Prior Art
The process of optical wavelength reconstruction is generally referred to as holography. Techniques for producing holograms vary, but in essence they entail what is shown in FIG. 1 as follows: a source beam of coherent light, usually a laser 1, is passed through a beam splitter 2 producing two distinct beams: an object beam 7 and a reference beam 8. With the aid of lenses 3 and 4, each beam of coherent laser light is spread to form a wavefront of light. The object beam 7 wavefront is directed at a mirror 5 which reflects the wavefront onto the object 6. The currently accepted recording device, film 10, then receives the object beam 7 reflected from the object 6 and reference beam 8 and records the image as a pattern on photographic film.
The reflected illumination from the object is in the form of expanding spherical wavefronts, derived from the interaction of the coherent light wavefront and every point on the object, producing an irregular wavefront that contains certain information about the object. When the second beam, the reference beam 8, from the same coherent light source, is directed to the recording device without being reflected from the object, the two beams form an interference pattern on the film. This interference pattern is formed by the constructive and destructive interference of the object and reference beam wavefronts on the film. This interference pattern, as shown in FIG. 2, is comprised of intensity variations due to variations in the phases and amplitudes of the two wavefronts. In summary, the recording and subsequent reillumination of an interference pattern of the object and reference beams of coherent light is a hologram.
Holograms differ from conventional photography in two important ways. Conventional photography records an image of reflected incoherent visible light by focusing the image, through the use of a lense, on film. When developed, this image is then visible to the naked eye using any standard non-coherent light source. A standard holographic recording uses no focusing device to form an image, but rather records the interference patterns of coherent light. When developed, a hologram produces a non-recognizable image when viewed by the naked eye under non-coherent light. The hologram can however, be illuminated by a coherent light source (using a reference wavefront) producing an interference pattern in which the original interference pattern is reconstructed, and when viewed gives an illusion which appears as if the original object is suspended in space.
An article by D. Gabor 161,777 (1948) and which appeared in Proceedings of the Royal Society. (London) A197,454 (1949) describes this type of optical reconstruction and states that images produced by this technique possess all the three-dimensional characteristics of the original object.